GF have been shown to secrete PGE2, IL-lB, IL-6 and IL-8 upon bacterial challenge. These molecules may contribute to periodontal attachment loss directly or indirectly by inducing local amplification of inflammatory and catabolic processes. Different bacterial species may preferentially stimulate secretion of these molecules by HGF in a disease-specific manner. This investigation tested the ability of A. actinomycetemcomitans (Aa) and C. rectus (Cr) to differentially stimulate secretion of PGE2, IL-lB, IL-6 and IL-8 by HGF extracted from healthy (H), adult periodontitis (AP), and localized juvenile periodontitis (LJP) subjects. HGF were harvested from medically healthy donors, 2 clinically free of periodontal disease, 2 Aa-infected AP and 2 Aa-infected LJP patients. Contact-inhibited HGF were prepared in 4-day, 96-well plate cultures. Formalin-killed whole bacterial cells (Aa JP2 and Cr ATCC 33238) at 109 cells/well were added and incubated. Culture supernatants were collected at 3, 6, 12, 24 and 48 h and analyzed using RIAs for PGE2, IL-lB, IL-6 and IL-8 (PerSeptive Diagnostics). Basal (unstimulated) cytokine levels did not differ among HGF types. PGE2 basal levels were somewhat elevated in AP and LJP HGF as compared to H. Aa did not stimulate secretion of PGE2 by H and AP HGF above basal levels, but stimulated LJP HGF significantly throughout the incubation time. Cr enhanced secretion levels of PGE2 by all HGF types but appeared to be more efficient in stimulating AP and LJP HGF. IL-lB secretion was not stimulated above basal levels by Aa or Cr in all HGF groups. Both Aa and Cr significantly stimulated IL-6 production. Aa was more efficient in stimulating LJP HGF, whereas Cr was more efficient with H and AP HGF. IL-8 secretion by H and AP HGF was not enhanced by Aa but was significantly stimulated in LJP HGF. Cr stimulated IL-8 secretion uniformly by all HGF. In general, Aa appeared to be more potent than Cr in stimulating LJP HGF, whereas Cr was more potent than Aa in stimulating H and AP HGF. In conclusion, different bacteria may contribute to the inflammatory characteristics of specific periodontal disease types by differentially stimulating cytokine and mediator production by HGF.